Oxidation of ammonia



Patented o... 27, 1925.

UNITED STATES CARLETON mums,- or xomcnnn; xnw was, nssronoa T anus r0 A conronn'rox or new mam. c

p "1,558,598 PATENT OFFICE.

OXIDATION OF AIHONIA.

in Drawing. Application filed April as, 1918,.Serial in. 231,014. Renewed January "is, 1925.

To all whom it may concern clair, in the count Be it known that .I, Cxnnnron ELLIS, a citizen of the United States, residing at Montof Essex and State of New Jersey, have invented certain new and useful Improvements in the Oxidation of Ammonia, of which the following is a speci- This invention relates'to a process of oxidizing ammonia to form nitrous acid, nitric acid, ammonium nitrate, nitrite and the like and to catalyzers adapted therefor, and relates particularly to the use of a particular class of catalyzers for thetreatment of a mixture of ammonia with air or oxygen, comprising exposure to a heated mass of catalytic material such for example as a material containing (or salt of) vanadic acid, or 'anadium-containing, or analogous acid, under conditions adapted for eflicient oxidation...

In the oxidation of ammonia especially with a powerful oxidizing catalyst such as platinum a good deal of difiiculty is' experienced in regulating the oxidationv so as to not burn a relatively large part of the ammonia to the state of water and free nitrogen and in the present invention it is one object to provide a group of cataly'tic agents capable of oxidizing ammonia to nitrogen oxides or to ammonlum nitrate as the case may be, without the production of any con-- siderable amounts of free nitrogen from nitrogen compounds.

A series of such catalytic compounds are found in the salts of vanadium (andparticularly those in which the vanadium is in the acid radical, notably vanadic acid) with the heavy metals, but in some cases the phosphate.

These catalyzers tend to efiect a more coniplete oxidation, forming oxids of nitrogen rather than a slight oxidation of the am-v monia molecule which would form free nitrogen.

In'the oxidation, of ammonia, in accordance with the presentdnvention, with such catalytic agents, a mixture of air and ammonia, (the latter being present in the gas mixture to the extent of about five to six per cent or more, by' volume) is passed into contact with the catalytic material which may be of a finely-divided nature and may be distributed on a carrier, or shaped "into example, in the manner analogous to that described in my Patent No. 1,227,044: patented May 22, 1917. In other words, by treating for example, the chloride of ametal (e. g. CoCl with the ammonium salt of the acidic material (e. g. ammonium vana- STER COMPANY,

the form of porous granular masses, as for date) the reaction takes placewith'the formation of ammonium chloride, which is eliminated by heating, leavinga highly porous. body, (perha s cobalt yanadate, or at any event a solid ody, preferably in a condition of intumescence containing cobalt as its base-forming metal and also containing vanadium functioning as the acid-forming element), which body is to be employedas the catalytic material, which material is pervious to gases. In preparing the catalyst in this example, the formation of cobalt vanadate may or may not be absolutely complete. V

Throughout this specification, examples of proportions of ammonia and air are given by volume. v

Granular porous masses produced as described above may be readily charged into a suitable catalytic chamber and afl'ord a very porous or penetrable bed through which a currentof ammonia-laden air may be passed freely so that no undue pressures are required to drive'the gases through the apparatus, although if desired the whole system may. be under superatmospheric pressure. A. superatmospheric pressure of one to ten atmospheres may be used.

The most desirable temperature ofthe reactionmass to produce a maximum yield, is around a low red heat but this varies somewhat with the character of the catalytic agent and the manner in which it is prepared. -The rate of flow of the gases also 1s regulated according to circumstances.

.For example, if the catalytic material is 'culty requiring increasing pressures and leading to disturbances caused by lack of proper adjustment which are undeslrable. While in somecases it may be feasible to use such asbestos-coated material in the present invention it is usually better to use the material in the form of granules, which ranules preferably are porous and these ragments or granules are packed into a catalytic chamber which preferably is placed in a vertical position in order to prevent settlement of the catalytic material leaving a freechannel at the top as not infrequently occurs when the catalytic material is placed in tubular horizontal catalytic chambers. By disposing such granular catalytic bodies in a vertical tube this difficulty is obviated.'

. oxygen.

The mixture of ammonia and air may be preheated ornot according to the pro-.

portions of the mixture and the size of the apparatus. Large masses of catalyzer and liable to overheat if the air content is low in which case cooling is necessary or desirable.

The regulation of the temperature in large masses of catalyzer is attained by introducing a mixture of air with ammonia in excess, and after the reaction has started at one end of the catalyzer chamber, additional air is added at one or more points in the 'catalyzer mass through distributing tubes, until a suflicient amount of air is introduced to completely oxidize the ammonia to the products desired. Thus the final air content may be represented by the equivalent of adding five or six per cent of ammonia to theair mixture entering the chamber. Or a much larger proportion of ammonia may be used so that the total air employed is precisely the equivalent of that required for the complete oxidation of ammonia to NO or N0 as desired. In other cases ammonia may be used in excess of the totalair employed in order to better control the temperature, and when pure nitrogen is required as a byproduct, whereby it is possible to more completely burn out-the The excess of ammonia or ammonium salt is duly removed or recovered. When the ammonia is .used in the exact proportion required for combination with the oxygen present to produce N0 an equilibrium is reached which prevents the complete union of oxygen, thereby causing the nitrogen to be contaminated with oxygen and unfit for use in the manufacture of ammonia by the syntheticproccss without resort to extensivepurification methods.

Nitrous oxide (N 0) is formed by heating ammonium nitrate. Hence if am-.

monium nitrate is formed in the catalytic conversion when an excess of ammonia is present with nitric and nitrous oxides there always is the possibility of decomposition caused by the high temperature to which the material is subjected, resulting in the formation of nitrous oxide which of course cannot be absorbed in alkaline solutions. In case such reaction goes on to an excessive degree under imposed conditions, the nitrous oxide may be separately collected. The oxidation of the ammonia also may form nitric oxide (NO) which in the presence of air eventually forms nitrogen tetroxide or peroxide (N 0,). Nltrogen peroxide reacts with nitric oxide to form nitrogen trioxide (N 0 which may be absorbed by alkali to yield nitrites.

Nitrogen peroxide with water forms nitric acid and liberates nitric oxide which in the presence of air is oxidized to nitrogen peroxide and ultimately the entire content of nitric oxide, in the presence of air and moisture, becomes converted into nitric acid.

As a specific example of the manufacture of a catalyst particularly adapted for use in the oxidation of ammonia according to the present invention, the following example is given Ammonium vanadate solution is mixed with cobalt chlorid solution, the mixture evaporated to dryness with constant stirring, and the dry mass heated up until the fumes of ammonium chlorid cease to be evolved. This produces highly porous, more or less granular product (perhaps cobalt vanadate), suitable for use in the process.

The following example of the oxidation of ammonia is given for the purpose of illustration.

The cobalt-vanadium containing catalyst prepared as above described, and in a porous granular state, is placed in a. vertical tube, in a heating furnace, where the same is heated up until the temperature of the catalyzer mass reaches about 600 to 700 C. Air to which 6% of NH gas has been added is then passed up through the catalyst, the air entering the catalyzer tube at about (1, and leaving at about 600 C. The pressure may be atmospheric, or somewhat above or below this. The gases, after cooling, may be led first into contact with an acid material to absorb unconverted ammonia, and then. either with or Without the addition of oxygen or air. the gases are washed with dilute-nitric acid and water (systematically) to produce nitric acid. The catalyst containing cobalt vanadate above referred to, in an intumesced condition has given very satisfactory results. The other cobalt compounds referred to are also satisfactory. The catalyst containing cobalt l5 -vention is not limited to these specific exvanadate can belconside d coma.

regarded as an intimate association haps complete chemical combination) 0 balt oxid with an oxid which increases its catalytic activity. To some extent, at least, the vanadium oxid orioxids of other acid- .forming metals capable of existingin several stages of oxidation canalso increase the catalytic activity of the oxids of the metals- It is of course understood that the inamples which are given for the purpose of illustration only.

To recapitulate. the invention relates to.

the process of oxidizing ammonia, specifically to form oxides of nitrogen and re lates particularly to the process comprising exposing, preferably at a low or dull heat, a mixture of ammonia and an oxygencontaining gas, such as air, to the action of an oxidizing catalyzer comprising a compound containing the oxides of at least two metals, one or both of which metals are capable of existing in more than one stage of oxidation, such for example, as cobalt vanadate, and the invention further comprises the process of oxidation of ammonia by an oxidation catalyst including metallic vanadates, especially as stated. thecobalt compound of vanadic acid. The invention also comprises a catalytic material adapted for the oxidation of ammonia to form nitrous acid and the like, which comprises a compound containing the oxides of at least two metals, one or both of which metals are capable of existing in more than one stage of oxidation and especially a com-' pound of the type of cobalt vanadate embracing compounds of the cobalt group with an oxide'capable' of increasing its catalytic activity, for example oxld of vanadium such I claim:

1. The process of oxidizing ammonia to form nitrous acid and the like whichcomprises passing a mixture contammg ammonia and air into contact with a eated 'catalyzer comprising granules of cobalt vanadate.

2. The process of ox1d1z1ng ammonia to the vanadium group appears as the acidforming element, such compound also containing ametal capable of existing in more than one stage .of oxidation-.

3. The process of oxidizing ammonia to form oxides of nitrogen which comprises passing a mixture containing ammonia and Q form acid, nitric acid, ammonium" oxygen, cobalt andfvanadiumggand mazgb e air into contact with a catalyzer comprising a vanadate of a heavy metal.

.4. The process of oxidizing ammonia to form oxides of nitrogen which comprises passing a-mlxture contam 'ng ammonia and an oxygen-containinggas into'contact with an oxidizing catalyzer in a form pervious to gases and maintained at a 'low' red heat;

said catalyzer comprising a compound of a,

metal of-the cobalt group with an oxygen acid of a metal capable of existing inmore than one stage of oxidation. i

The process of oxidizing ammonia to folln oxides-of nitrogen which. comprises pa sing a mixture containing ammonia and an pxygen-containing as into contact with an oxidizing catalyzer aving a form highly peryious to gases and being maintained at a dull red heat; said catalyzer comprising a compound containing two metals one of which exists in said compound as the acidforming element, and both of which. are

capable of existing with different valencies,

in more than one stage of oxidation.

6. The process of ,oxidizing ammonia to form oxides of nitrogen which comprises passing a mixture of ammonia and an oxygen-containing gas into contact with a catalyzer comprising a compound of cobalt with an oxygen acid of a metal capable of existing in more than one stage of oxidation.

7. The process of oxidizing 'ammonia to form oxides of nitrogen which comprises passing a mixture containing ammonia and an oxygen-containing gas into contact with" I a catalyzer comprising a compound of a metal of the cobalt group with an oxygen acid of a metal capable of existing in more part of sai catalyzer being in a form" readily pervious to gases.

8. The process of oxidizing ammonia to .form oxides of nitrogen WlllCll comprlses passlng a mlxture containing ammonia and than one sta e of oxidation; at least some a metal of the cobalt group with an oxygen acid of a metalcapable of existing in more than one stage of oxidation.

9. The process of oxidizing ammonia to form oxides of nitrogen which comprises passing a mixture containing ammonia and an oxygen-containing gas into contact with a'highly porous, gas-pervious catalyzer comprising a comfiound of the oxides of at least two metals,'a of which are capable of existing in more than one stage of oxidation, all of which have atomic weights not less than 40.

10. The process of oxidizing ammonia to .form oxides of nitrogen which comprises passing a mixture of gases containing ammonia and oxygen into contact with a substantially gas-pervious catalyzer maintained at a temperature of at least a dull red heat; Said catalyzer comprising a compound of the oxides of two metals, both' of which are capable of existing in more than one stage of oxidation, the metal in the acid radical havin an atomic weight of from 51 to 52.

- 11. The process of oxidizing ammonia to form oxides of nitrogen which comprises passing a mixture containing ammonia and an oxygen containing gas into contact with a catalyzer comprising a compound of a metal of the cobalt roup with an oxygen acid of a metal capa is of existing in more,

than one stage of oxidation.

12. The process of oxidizing ammonia to form oxides of nitrogen which comprises passing a mixturecontaining ammonia and oxy en-containing gas into contact with a cata yzer comprising a compound 'of the oxides of at least two metals, each of which metals is capable of formin more than one oxide, and at least one of w ich metals has an atomic weight between 51 and 63.

13. The process of oxidizing ammonia to form oxides of. nitrogen wluch comprises passing a mixture'containing ammonia and oxygen containing gas into contact with a porous granular catalyzer comprising a compound "of the oxides of at least two metals, each of which metal is capable of forming more than one oxide, and the metal which acts as the acid-forming element being embraced within the fifth and sixth oupsof theperio'dic system, with an atomic weight between 51 and 96.

14. The process of oxidizing ammonia to form oxides of nitrogen, etc., which comprises passing a mixture containin ammonia and air through a vertically disposed catalytic mass whose length is greater than its diameter and which comprises porous granular fragmental catalytic material comprising a compound of one heavy metal oxid with another heavy metal oxid each of said metals being capable of'existing in more than one stage of oxidation, one of the said metals being embraced within the fifth and sixth groups of the periodic classification, such metals having atomic weights between 51 and 63.6.

15. The process of oxidizing ammonia to form oxides of nitrogen, etc. which comprises passing a mixture of ammonia and 16. Theprocessof oxidizing ammonia toform oxides of nitrogen, etc., which comprises passing a. mixture of ammonia and air through a' catalytic mass which comprises porous fragmental catalytic material comprisin cobalt vanadate.

17. he process of oxidizing ammonia to form oxides of nitrogen, etc., which comprises passing a mixture of ammonia and air through a mass of catalytic material of a highly porous nature composed of a metal vanadate unassociated with an inert carrier or sup orting material.

18. he process of oxidizing ammonia to form oxides of nitrogen, etc., which comprises pxassing a mixture of ammonia and air throug a mass of material consisting of highly porous granules of a catalytic compoun said compound being composed of oxids of apluralit of metals each capable of form1ng more t an one oxid, a salt contaming a plurality of metals, one of which acts as the acid-forming element and pears in the fifth to sixth roups of periodic system and which as an atomic weight between 51 and 96, and the base forming material in said salt having'an atomic weight between 40.07 and 197.

-19. The process of oxidizing ammonia to form oxides of nitrogen, etc., which comprises passing a "gas current containing oxygen and ammonia through a pervious mass of intumesced material comprising an oxidizing catalyst; comprising a salt containing a plurality of metals, one of which acts as the acid-forming element and occurs in the fifth to sixth groups of the eriodic system and has an atomic weight tween 51 and 96.

20. A process of oxidizing ammonia which comprises passing a mixture com rising ammonia and oxygen in contact wit a catalyst containing a plurality of metals in the form of a'chemical com ound, one of said metals occurring in the fi h to sixth ups of the periodic system, and all of suc metals havmg atomic weights between40 and 197.

21. In the oxidation of ammonia, the step' of assing a mixture containing ammonia an air, in contact with a catalyzer contain-' of the fifth group of the periodic classification, and oxygen, such three elements each being in a combined state.

23. In the oxidation of ammonia, the step of passing a mixture containing ammonia and air in contact with a porous catalyst comprising cobalt and oxygen, and an activating agent.

24. In the oxidation of ammonia, the step of assing a mixture containing ammonia and air in contactwith a catalyzer containing oxygen, cobalt, and a material which is capable of increasing the catalytic activity.

25. In the oxidation of ammonia, the step of passing a mixture containing ammonia and air in contact with a orous catal st comprising oxygen and bot cobalt an a metal which is capable of acting as an:acid forming oxide.

26. In the oxidation of-ammonia, the step of passing a mixture containing ammonia and air, in contact with a catalyzer containing 0 gen, a metal of the cobalt group, and an aci -forming elementwhich is capable of increasing its catalytic activity.

27. In the oxidation of ammonia, the process which comprises passing ammonia and a gas containing free oxygen, in contact with a catalyst containing oxygen, cobait and vanadium.

In testimony whereof I have aflixed my signature.

CARLETON ELLIS. 

